Computational fluid dynamics-based design and in vitro characterization of a novel pediatric pump-lung

BACKGROUND

Although extracorporeal membrane oxygenation (ECMO) has been used to provide temporary support for pediatric patients suffering severe respiratory or cardiac failure since 1970, ECMO systems specifically designed for pediatric patients, particularly for long-term use, remain an unmet clinical need. We sought to develop a new pediatric ECMO system, that is, pediatric pump-lung (PPL), consisting of a unique cylinder oxygenator with an outside-in radial flow path and a centrifugal pump.

METHODS

Computational fluid dynamics was used to analyze the blood fluid field for optimized biocompatible and gas exchange performances in terms of flow characteristics, hemolysis, and gas transfer efficiency. Ovine blood was used for in vitro hemolysis and gas transfer testing.

RESULTS

Both the computational and experimental data showed that the pressure drop through the PPL's oxygenator is significantly low, even at a flow rate of more than 3.5 L/min. The PPL showed better hemolysis performance than a commercial ECMO circuit consisting of the Quadrox-iD pediatric oxygenator and the Rotaflow pump at a 3.5 L/min flow rate and 250 mm Hg afterload pressure. The oxygen transfer rate of the PPL can reach over 200 mL/min at a flow rate of 3.5 L/min.

CONCLUSIONS

The PPL has the potential to provide adequate blood pumping and excellent respiratory support with minimal risk of hemolysis for a wide range of pediatric patients.

Computational optimization of delivery parameters to guide the development of targeted Nasal spray

Airborne transmission by droplets and aerosols is known to play a critical role in the spread of many viruses amongst which are the common flu and the more recent SARS-CoV-2 viruses. In the case of SARS-CoV-2, the nasal cavity not only constitutes an important viral entry point, but also a primary site of infection (Sungnak W. et al. Nat. Med. 26:681-687. https://doi.org/10.1038/s41591-020-0868-6 , 2020).. Although face masks are a well-established preventive measure, development of novel and easy-to-use prophylactic measures would be highly beneficial in fighting viral spread and the subsequent emergence of variants of concern (Tao K. et al. Nat Rev Genet 22:757-773. https://doi.org/10.1038/s41576-021-00408-x , 2021). Our group has been working on optimizing a nasal spray delivery system that deposits particles inside the susceptible regions of the nasal cavity to act as a mechanical barrier to impede viral entry. Here, we identify computationally the delivery parameters that maximize the protection offered by this barrier. We introduce the computational approach and quantify the protection rate obtained as a function of a broad range of delivery parameters. We also introduce a modified design and demonstrate that it significantly improves deposition, thus constituting a viable approach to protect against nasal infection of airborne viruses. We then discuss our findings and the implications of this novel system on the prevention of respiratory diseases and targeted drug delivery.

Portable Device for Measuring Blood Test Hemolyzed Samples Based on Computer Vision and Neural Network

Hemolysis is a challenging problem and still represents a frequent source of errors in blood test laboratory practice. Due to the broad and heterogeneous bias induced in the measurement of several parameters by hemolysis, inaccurate results may be reported, and the patient may be required to repeat sample collection, delaying diagnosis. Existing automated laboratory devices including hemolysis detection are not suitable for lower volume and smaller sample collection sites. In many situations, hemolysis is still detected by visual inspection of the sample after centrifugation, during the blood test pre-analytical stage. Visual inspection is highly dependent on a qualified workforce, subjective to interpretation discrepancies, and thus difficult to standardize. The paper aims to describe the design and performance of a portable device for measuring hemolyzed samples based on computer vision and neural network. The results indicate that the device provides hemolysis indexes with sufficient accuracy to guide laboratory decision in the blood test pre-analytical stage.

Mesh sensitivity analysis for quantitative shear stress assessment in blood pumps using computational fluid dynamics

The reduction of excessive, nonphysiologic shear stresses leading to blood trauma can be the key to overcome many of the associated complications in blood recirculating devices. In that regard, Computational Fluid Dynamics (CFD) are gaining in importance for the hydraulic and hemocompatibility assessment. Still, direct hemolysis assessments with CFD remain inaccurate and limited to qualitative comparisons rather than quantitative predictions. An underestimated quantity for improved blood damage prediction accuracy is the influence of near-wall mesh resolution on shear stress quantification in regions of complex flows. This study investigated the necessary mesh refinement to quantify shear stress for two selected, meshing sensitive hotspots within a rotary centrifugal blood pump. The non-dimensional mesh characteristic number y+, which is known in the context of turbulence modelling, underestimated the maximum wall shear stress by 60% on average with the recommended value of 1, but was found to be exact below 0.1. To evaluate the meshing related error on the numerical hemolysis prediction, three-dimensional simulations of a generic centrifugal pump were performed with mesh sizes from 3 to 30 million elements. The respective hemolysis was calculated using an Eulerian scalar transport model. Mesh insensitivity was found below a maximum y+ of 0.2 necessitating 18 million mesh elements. A meshing related error of up to 25% was found for the coarser meshes. Further investigations need to address: 1) the transferability to other geometries and 2) potential adaptions on blood damage estimation models to allow better quantitative predictions.

Computational Parametric Study of the Axial and Radial Clearances in a Centrifugal Rotary Blood Pump

In centrifugal rotary blood pumps (RBP), clearances are a critical parameter in determining blood trauma. This study investigates the effect of axial clearance (Cax) and radial clearance (Crad) on the hydrodynamic and hemolytic performance of a centrifugal RBP. A centrifugal pump was parameterized so that it could be defined by geometric variables Cax and Crad. Optimal Latin hypercube sampling was used to determine design points based on Cax, Crad, and rotor speed (ω). For each design point, a computational simulation was conducted to determine efficiency (η) and normalized index of hemolysis (NIH). Next, a response surface (RS) was created to estimate these performance parameters based on the design variables. The results show that for a given Cax, when Crad is decreased, η increases until Crad = 0.15 mm, beyond which η deceases. For a given Crad, Cax has a unimodal relationship with η. The NIH has a unimodal relationship with both Cax and Crad. The mechanisms behind these relationships were investigated by various analytical methods. It was found that vortices in the secondary flow paths were a critical factor in determining efficiency and hemolysis. The optimal clearance values discerned in this study are only valid for the specific impeller geometry and operating conditions analyzed.

Machinability and Optimization of Shrouded Centrifugal Impellers for Implantable Blood Pumps

This paper describes the use of analytical methods to determine machinable centrifugal impeller geometries and the use of computational fluid dynamics (CFD) for predicting the impeller performance. An analytical scheme is described to determine the machinable geometries for a shrouded centrifugal impeller with blades composed of equiangular spirals. The scheme is used to determine the maximum machinable blade angles for impellers with three to nine blades in a case study. Computational fluid dynamics is then used to analyze all the machinable geometries and determine the optimal blade number and angle based on measures of efficiency and rotor speed. The effect of tip width on rotor speed and efficiency is also examined. It is found that, for our case study, a six- or seven-bladed impeller with a low blade angle provides maximum efficiency and minimum rotor speed.

Multi-objective optimization of pulsatile ventricular assist device hemocompatibility based on neural networks and a genetic algorithm

PURPOSE

Given the benefit of pulsatile blood flow for perfusion of coronary arteries and end organs, pulsatile ventricular assist devices (VADs) are still widely used as paracorporeal mechanical circulatory support devices in clinical applications. However, poor hemocompatibility limits the service period of the VADs. Most previous improvements on VAD hemocompatibility were conducted by trial-and-error CFD analysis, which does not easily arrive at the best solution.

METHODS

In this paper, a multi-objective optimization method integrating neural networks and NSGA-II (Non-dominated Sorted Genetic Algorithm-II) based on FSI simulation was developed and applied to a pulsatile VAD to optimize its hemocompatibility. First, the VAD blood chamber was parameterized with the principal geometrical parameters. Three hemocompatibility indices including hemolysis, platelet activation, and platelet deposition were chosen as goal functions. The neural networks were built to fit the nonlinear relationship between goal functions and geometrical parameters. Next, a multi-objective optimization algorithm (NSGA-II) was used to search out the Pareto optimal solutions in the built neural networks. Finally, the best compromise solution was selected from the Pareto optimal solutions by a fuzzy membership approach and validated by FSI simulation.

RESULTS

The best compromise solution simultaneously possesses an acceptable hemolysis index, platelet activation index, and platelet deposition index, and the corresponding relative errors between the indices predicted by optimization algorithm and the one calculated by FSI simulations are all less than 5%.

CONCLUSIONS

The results suggest that the proposed multi-objective optimization method has the potential for application in optimizing pulsatile VAD hemocompatibility, and may also be applied to other blood-wetted devices.

Biocompatibility assessment of a long-term wearable artificial pump-lung in sheep

The purpose of this study was to assess the biocompatibility of a newly developed long-term wearable artificial pump-lung (APL) in a clinically relevant ovine animal model. The wearable APL device was implanted in five sheep through left thoracotomy. The device was connected between the right atrium and pulmonary artery and evaluated for 30 days. Three sheep were used as the sham control. Platelet activation was assessed by measuring platelet surface P-selectin (CD62P) expression with flow cytometry and plasma soluble P-selectin with an enzyme-linked immunosorbent assay. Thrombotic deposition on the device components and hollow fiber membranes were analyzed with digital imaging and scanning electron microscopy. Surface P-selectin of the APL and sham groups changed significantly over the study period, but without significant differences between the two groups. Soluble P-selectin for the two groups peaked in the first 24 h after the surgery. Soluble P-selectin of the APL group remained slightly elevated over the study period compared to the presurgical baseline value and was slightly higher compared to that of the sham group. Plasma free hemoglobin remained in the normal ranges in all the animals. In spite of the surgery-related alteration in laboratory tests and elevation of platelet activation status, the APL devices in all the animals functioned normally (oxygen transfer and blood pumping) during the 30-day study period. The device flow path and membrane surface were free of gross thrombus. Electron microscopy images showed only scattered thrombi on the fibers (membrane surface and weft). In summary, the APL exhibited excellent biocompatibility. Two forms of platelet activation, surgery-related and device-induced, in the animals implanted with the wearable APL were observed. The limited device-induced platelet activation did not cause gross thrombosis and impair the long-term device performance.